Dye fixing agent for water-color ink, ink jet recording medium and porous hydrotalcite compound

ABSTRACT

A dye fixing agent for water-color ink to be contained in the water-color ink accepting layer of an ink jet recording medium having an water-color ink accepting layer formed on a substrate, which is a hydrotalcite compound containing a silicic acid anion and a sulfuric acid ion, or a silicic acid anion as an anion(s).  
     An ink jet recording medium comprising the dye fixing agent for water-color ink formed on a substrate.  
     The dye fixing agent for water-color ink of the present invention is excellent in the fixability of water-color ink, the resolution of an image recorded on a medium, water resistance and light resistance.

DETAILED DESCRIPTION OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a water-soluble dye fixing agentwhich can be used in an ink jet recording medium to form a recordedimage using water-color ink containing a water-soluble dye and to an inkjet recording medium comprising the same. Particularly, it relates to adye fixing agent for ink jet recording media which is excellent in thefixability of water-color ink and the resolution, water resistance andlight resistance of an image recorded on an medium and to an ink jetrecording medium comprising the same. The present invention also relatesto a novel porous hydrotalcite compound.

[0003] 2. Prior Art

[0004] Along with progress made in personal computers and digitalcameras, displayed images have been recorded on printing paper likesilver salt-based photographs. An image forming system called “ink jetrecording system” is known as a system for recording such displayedimages. Since this ink jet recording system has various features such aslittle noise, high-speed recording, multi-color recording, wideapplicability of a recorded pattern and the elimination of need fordevelopment and fixing, it is used in many fields.

[0005] The principle of the ink jet recording system is that an inksolution is ejected from a nozzle by a drive source such as electricfield, heat or pressure and transferred to the accepting layer ofprinting paper. The ink solution comprises a dye, water, polyhydricalcohol and the like and a water-soluble substantive dye or acidic dyeis used mainly as the dye.

[0006] The printing paper is constructed by forming a dye acceptinglayer on a substrate and coated paper, glossy paper, glossy film, OHPfilm or the like is used as the substrate according to need. Theaccepting layer comprises a water-soluble polymer having excellentaffinity for a dye, organic or inorganic filler and other auxiliarysubstances whose blending ratio is suitably adjusted to control thepermeability of the dye and to suppress a blurred image.

[0007] Images obtained by this ink jet recording system now have highdefinition thanks to recent marked progress made in the quality of theimages and the improvement of dot density and the glossiness of theaccepting layer, so as to have as high quality as that of a silver-basephotograph at a visible range.

[0008] JP-A 61-135785 (the term “JP-A” as used herein means an“unexamined published Japanese patent application”) (JP-B 4-15747) (theterm “JP-B” as used herein means an “examined Japanese patentpublication”) proposes that the light resistance of a substrate isimproved by using synthetic silica and a hydrotalcite consisting of acarbonic acid ion as a divalent anion in a dye accepting layer.

PROBLEMS TO BE SOLVED BY THE INVENTION

[0009] The substantive dye or acidic dye contained in the ink solutionused in the ink jet system is retained in the accepting layer byinteraction such as van der Waals binding force and hydrogen bond withthe constituent components of the accepting layer after it has beentransferred to the accepting layer as shown by the dyeing theory ofdyes. Therefore, when an image formed on the accepting layer iscontacted to a solvent or resin having high affinity for the dye or whenheat energy large enough to cancel the interaction is supplied, theelution or transfer of the dye is induced, thereby causing suchinconvenience as a blurred image. That is, the dye transferred to theaccepting layer does not show completely stable fixability like a silversalt-based photograph. The same is said of stationery using asubstantive dye or acidic dye and general image forming materials usedfor printing and the like.

MEANS FOR SOLVING THE PROBLEMS

[0010] To cope with this, the inventors of the present invention haveconducted studies to develop a fixing agent capable of stably fixing adye in the water-color ink accepting layer of an ink jet recordingmedium having a water-color ink accepting layer formed on a substrate.That is, the inventors have conducted studies to develop a fixing agentwhich prevents the elution or transfer of a dye even when it iscontacted to a solvent or a resin having high affinity for the dye orwhen heat is supplied to the dye after the dye is transferred to theaccepting layer and fixed.

[0011] The inventors have paid attention to a hydrotalcite compound as afixing agent, synthesized various hydrotalcite compounds andinvestigated the dye fixing stabilities of the compounds.

[0012] As a result, they have found that the type of an anion(s) forminga hydrotalcite compound is closely related to dye fixing stability andthat a hydrotalcite compound having both a silicic acid anion and asulfuric acid ion, or a silicic acid anion as an anion(s) has extremelystable fixability for a dye. It has also been found that when thishydrotalcite compound is used as a fixing agent, a high-definition imagerecording medium can be obtained. The hydrotalcite compound containing asilicic acid anion and a sulfuric acid ion, or a silicic acid anion asan anion(s) in a certain amount and having specific pore characteristicshas more stable fixability.

[0013] According to the present invention, there is provided a dyefixing agent for water-color ink to be contained in the water-color inkaccepting layer of an ink jet recording medium having a water-color inkaccepting layer formed on a substrate, which is a hydrotalcite compoundcontaining a silicic acid anion and a sulfuric acid ion, or a silicicacid anion as an anion(s).

[0014] According to the present invention, there is further provided anink jet recording medium which comprises a hydrotalcite compoundcontaining the above specific anion(s) as a dye fixing agent.

[0015] The dye fixing agent for water-color ink and the ink jetrecording medium comprising the same of the present invention will bedescribed in detail hereinbelow.

[0016] The hydrotalcite compound used as the dye fixing agent forwater-color ink of the present invention is characterized in that itcontains a silicic acid anion and a sulfuric acid ion, or a silicic acidanion as an anion(s) forming the compound. More specifically, thehydrotalcite compound is more advantageously a hydrotalcite compoundwhich contains a silicic acid anion and a sulfuric acid ion, or asilicic acid anion in an amount of 10 to 98 mol %, preferably 20 to 98mol % based on the total of all the anions.

[0017] The silicic acid anion is SiO₃ ²⁻, HSiO₃ ⁻, Si₂O₅ ²⁻ or HSi₂O₅ ⁻and the sulfuric acid ion is SO₄ ²⁻.

[0018] When the hydrotalcite compound used in the present inventioncontains a silicic acid anion and a sulfuric acid ion as anions, itcontains the silicic acid anion in an amount of 5 to 100 mol %,preferably 10 to 100 mol %, particularly preferably 20 to 100 mol %based on the total of the silicic acid anion and the sulfuric acid ion.

[0019] It is advantageous that the hydrotalcite compound used in thepresent invention should have an average particle diameter measured by alaser diffraction scattering method of 0.1 to 10 μm, preferably 0.5 to10 μm.

[0020] The hydrotalcite compound used in the present invention ispreferably a compound represented by the following formula (I).

M^(II) _(1−x)Al_(x)(OH)₂(A₁ ^(n−))_(a)(A₂ ^(m−))_(b) .yH₂O  (I)

[0021] wherein M^(II) is Mg²⁺ or/and Zn²⁺, A₁ ^(n−) is a silicic acidanion having a valence of n and a sulfuric acid ion (SO₄ ²⁻), or asilicic acid anion having a valence of n, with the proviso that thesilicic acid anion having a valence of n is an anion selected from thegroup consisting of SiO₃ ²⁻, HSiO₃ ⁻, Si₂O₅ ²⁻ and HSi₂O₅ ⁻, A₂ ^(m−) isan anion selected from the group consisting of CO₃ ²⁻, NO₃ ⁻, Cl⁻ andOH⁻, x and y satisfy 0.15<x≦0.80 and 0<y<2, and a and b satisfy0.15<na+mb≦0.80.

[0022] In the above formula (I), M^(II) is Mg or/and Zn but it ispreferably Mg alone or a mixture of Mg²⁺ and Zn²⁺ (solid solution). WhenM^(II) is a mixture of Mg and Zn, the amount of Zn is preferablyequivalent to or less than Mg.

[0023] As described above, the hydrotalcite compound used in the presentinvention is characterized in that it contains a specific anion(s) in aspecific proportion to the total of all the anions. In the above formula(I), all the anions are represented by (A₁ ^(n−)+A₂ ^(m−)) and thehydrotalcite compound of the above formula (I) in which the proportion(A₁ ^(n−)/(A₁ ^(n−)+A₂ ^(m−))) of the silicic acid anion and thesulfuric acid ion, or the silicic acid anion, represented by A₁ ^(n−) tothe total of all the anions is 10 to 98 mol %, preferably 20 to 98 mol %is used. Since it is difficult to obtain a hydrotalcite compound of theabove formula (I) in which all the anions are A₁ ^(n−), the upper limitof the proportion of A₁ ^(n−) to the total of all the anions is 98 mol%. When the proportion of A₁ ^(n−) is smaller than 10 mol %, a fixingagent having low dye fixing stability is obtained disadvantageously.

[0024] The hydrotalcite compound represented by the above formula (I)includes hydrotalcite compounds represented by the following formulas(I-a) and (I-b) based on X and the total amount of all the anions in theformula.

M^(II) _(1−x)Al_(x)(OH)₂(A₁ ^(n−))_(a)(A₂ ^(m−))_(b) .yH₂O  (I-a)

[0025] wherein M^(II) is Mg²⁺ or/and Zn²⁺, A₁ ^(n−) is a silicic acidanion having a valence of n and a sulfuric acid ion (SO₄ ²⁻), or asilicic acid anion having a valence of n, with the proviso that thesilicic acid anion having a valence of n is an anion selected from thegroup consisting of SiO₃ ²⁻, HSiO₃ ⁻, Si₂O₅ ²⁻ and HSi₂O₅ ⁻, A₂ ^(m−) isan anion selected from the group consisting of CO₃ ²⁻, NO₃ ⁻, Cl⁻ andOH⁻, x and y satisfy 0.50<x≦0.80 and 0<y<2, and a and b satisfy0.50<na+mb≦0.80.

M^(II) _(1−x)Al_(x)(OH)₂(A₁ ^(n−))_(a)(A₂ ^(m−))_(b) .yH₂O  (I-b)

[0026] wherein M^(II) is Mg²⁺ or/and Zn²⁺, A₁ ^(n−) is a silicic acidanion having a valence of n and a sulfuric acid ion (SO₄ ²⁻), or asilicic acid anion having a valence of n, with the proviso that thesilicic acid anion having a valence of n is an anion selected from thegroup consisting of SiO₃ ²⁻, HSiO₃ ⁻, Si₂O₅ ²⁻ and HSi₂O₅ ⁻, A₂ ^(m−) isan anion selected from the group consisting of CO₃ ²⁻, NO₃ ⁻, Cl⁻ andOH⁻, x and y satisfy 0.15<x≦0.50 and 0<y<2, and a and b satisfy0.15<na+mb≦0.50.

[0027] It has been discovered that the hydrotalcite compound representedby the above formula (I-a) is a novel compound and is superior in dyefixing stability to the hydrotalcite compound of the above formula (I-b)and other hydrotalcite compounds and can provide a recording mediumwhich gives a high-definition image.

[0028] The hydrotalcite compound represented by the above formula (I-a)has a large surface area of each particle and excellent porecharacteristics. It is considered that a dye is easily fixed and thefixed dye can be stably existent because the hydrotalcite compound has alarge pore volume and a small average pore radius in particular.

[0029] That is, the hydrotalcite compound represented by the aboveformula (I-a) has the following characteristic properties (1) to (3):

[0030] (1) Its specific surface area measured by a BET method is 50 to400 m²/g, preferably 100 to 300 m²/g.

[0031] (2) Its total pore volume measured by an N₂ gas adsorption methodis 0.50 to 2.00 ml/g, preferably 0.7 to 1.6 ml/g.

[0032] (3) Its average pore radius measured by the N₂ gas adsorptionmethod is 4 to 15 nm, preferably 7 to 10 nm.

[0033] The hydrotalcite compound of the formula (I-a) has an averageparticle diameter measured by the laser diffraction scattering method of0.1 to 10 μm, preferably 0.5 to 10 μm and a unit layer interval of 8 to12 Å.

[0034] A hydrotalcite compound containing a silicic acid anion and asulfuric acid ion, or a silicic acid anion as an anion(s) is used as thedye fixing agent of the preset invention. This hydrotalcite compound ispreferably a compound represented by the above formula (I), the mostpreferably a compound represented by the above formula (I-a).

[0035] The hydrotalcite compound represented by the above formula (I-a)is a novel compound and has been unknown. Since the hydrotalcitecompound represented by the above formula (I-a) is more porous and moreexcellent in pore characteristics, it has extremely excellentcharacteristic properties as a dye fixing agent in addition to thecharacteristic properties of anions.

[0036] Accordingly, the hydrotalcite compound containing a silicic acidanion and a sulfuric acid ion, or a silicic acid anion as a dyeabsorbent in the present invention has all the above advantages, therebymaking it possible to retain dye molecules between layers, therebystabilizing the dye molecules, and to obtain an image having excellentink absorptivity, resolution, water resistance and light resistance.

[0037] In the ink jet recording medium of the present invention, coatingsolution constituting substances other than the dye fixing agent forwater-color ink will be described hereinbelow. To form a dye acceptinglayer on the substrate, a coating solution containing the dye fixingagent of the present invention is used. The coating solution comprises apolymer adhesive, additives and a solvent which are known per se as themain ingredients in addition to the dye fixing agent. It may furthercontain an inorganic or organic pigment as required. The ink jetrecording medium of the present invention may consist of a single layeror multiple layers and the substrate of the ink jet recording medium maybe subjected to a corona treatment or anchor coat treatment to improveadhesion. The accepting layer may be a single layer or multi-layer asrequired.

[0038] An inorganic or organic pigment may be used as an auxiliary inthe accepting layer as required. Examples of the pigment includeinorganic pigments such as synthetic silica, colloidal silica, cationiccolloidal silica, alumina sol, pseudo-boehmite gel, talc, kaolin, clay,baked clay, zinc oxide, zinc sulfide, zinc carbonate, tin oxide,aluminum oxide, aluminum hydroxide, aluminum silicate, calciumcarbonate, calcium sulfate, calcium silicate, satin white, bariumsulfate, titanium dioxide, magnesium silicate, magnesium carbonate,magnesium oxide, smectite, lithopone, mica, zeolite and diatomaceousearth; and organic pigments such as styrene-based plastic pigments,acrylic plastic pigments, microcapsuled plastic pigments, urearesin-based plastic pigments, melamine resin-based plastic pigments,benzoguanamine-based plastic pigments and acryl nitrile-based plasticpigments all of which are known per se in the field of general coatedpaper. A suitable pigment may be selected appropriately from these andused.

[0039] Examples of the polymer adhesive include (a) starches such asstarch, oxidized starch, etherified starch and cationized starch; (b)cellulose derivatives such as methyl cellulose, carboxymethyl cellulose,hydroxyethyl cellulose, hydroxypropyl cellulose and hydroxypropylmethylcellulose; (c) proteins such as gelatin, casein, soybean protein andsynthetic protein; (d) natural and semi-synthetic adhesives such asagarose, guar gum, chitosan and soda alginate; (e) polyvinyl alcoholderivatives such as polyvinyl alcohol, cationic polyvinyl alcohol andsilicon-containing polyvinyl alcohol; (f) synthetic, water-soluble andsolvent-soluble adhesives such as polyethyleneimine-based resins,polyvinylpyrrolidone-based resins, poly(meth)acrylic acid and copolymersthereof, maleic anhydride-based resins, acrylamide-based resins,(meth)acrylate-based resins, polyamide-based resins, polyurethane-basedresins, polyester-based resins, polyvinyl butyral-based resins, alkydresins, epoxy-based resins, epichlorohydrin-based resins, urea resinsand melamine resins; (g) conjugated diene-based latices such asstyrene-butadiene copolymer and methyl methacrylate-butadiene copolymer,acrylic polymer latices such as acrylate and methacrylate polymers andcopolymers, vinyl-based polymer latices such as ethylene-vinyl acetatecopolymer, and modified polymer latices containing a functional groupsuch as anionic group or/and cationic group thereof; and (h) conductiveresins typified by polyvinylbenzyltrimethylammonium chloride,polydiallyldimethylammonium chloride,polymethacryloyloxyethyl-β-hydroxyethyldimethylammonium chloride andpolydimethylaminoethyl methacrylate hydrochloric acid salts. Thesepolymer adhesives known in this technical field are used alone or incombination.

[0040] Various additives may be added in limits that do not preventfixability. The additives include conventionally known additives whichare commonly used, such as a dispersant, anti-foaming agent, thickener,ultraviolet light absorbent, fluorescent whitening agent, antioxidant,water resisting agent, surfactant, fluidity modifier, heat stabilizer,foam-inhibitor, foaming agent, tackifier, pH control agent, penetrant,wetting agent, heat gelling agent, lubricant, coloring agent,antiseptic, mildew-proofing agent, antistatic agent and crosslinkingagent.

[0041] Preferred examples of the solvent of the coating solution includelower alcohols such as methyl alcohol, ethyl alcohol and propyl alcohol;glycols such as ethylene glycol, diethylene glycol, triethylene glycoland dioxane; lower alkyl esters such as methyl acetate and ethylacetate; water-soluble organic solvents such as acetonitrile anddimethyl acetamide; and water. These solvents may be used alone or inadmixture of two or more.

[0042] Woodfree paper, medium-grade woodfree paper, coated paper, artpaper, cast coated paper, paper board, synthetic resin laminated paper,metal deposited paper, synthetic paper, white film or the like is usedas the substrate of a recording medium which does not need to transmitlight whereas glass or a film of polyethylene terephthalate, polyester,polystyrene, polyvinyl chloride, polymethyl methacrylate, polycarbonate,polyimide, cellulose triacetate, cellulose diacetate, polyethylene orpolypropylene, such as an OHP sheet is used as the substrate of a lighttransmitting recording medium. The amount of the dye fixing agent is 10to 90 wt %, preferably 15 to 90 wt % based on the total of solids (dyefixing agent, polymer adhesive, solid additives, pigment, etc.)constituting the accepting layer. When the amount of the dye fixingagent is too large, the accepting layer lacks flexibility and when theamount is too small, the accepting layer becomes inferior in dyefixability.

[0043] The method and means of forming a water-color ink accepting layerare not particularly limited and a suitable method may be employedaccording to the material of the substrate. The most common substratecoating method uses a bar coater, roll coater, air knife coater, bladecoater, rod blade coater, brush coater, curtain coater, gravure coater,flexographic coater, cast coater, die coater, lip coater, size press orspray.

[0044] In addition to the above method in which a recording medium isobtained by forming a dye accepting layer on the substrate, there isanother method in which a dye fixing agent is retained in entangledfibers and between them in the case of a recording medium comprising adye accepting layer and a substrate both of which are integrated witheach other, for example, pulp such as paper. An excellent recorded imageforming material can be obtained by containing the dye fixing agent ofthe present invention in a substrate itself including a surface thereof.

[0045] A coating solution is prepared by using the above dye fixingagent, polymer adhesive, additives, pigment and solvent.

BRIEF DESCRIPTION OF THE DRAWING

[0046]FIG. 1 is a diagram showing the acid dye adsorption isotherms ofhydrotalcite compounds obtained in Example 1 and Comparative Example 1in the present invention.

EXAMPLES

[0047] The following examples are given to further illustrate thepresent invention.

[0048] In the examples, the measurement and evaluation of physicalproperties were carried out as follows.

[0049] (1) The BET specific surface area (m²/g), total pore volume(ml/g) and average pore radius (nm) of a hydrotalcite compound(particles) were obtained from N₂ gas adsorption and desorption curvesusing the BELSORP 28SA gas adsorption apparatus of Nippon Bell Co., Ltd.after a measurement sample was maintained at 110° C. and 2.7×10⁻¹ Pa orless for 3 hours as a pre-treatment. The total pore volume is the totalvolume of pores having a radius of 1 to 100 nm.

[0050] (2) The average particle diameter (μm) of a hydrotalcite compound(particles) was measured by the LA-910 laser diffraction/scatteringsystem particle size distribution measuring instrument of HORIBA Co.,Ltd.

[0051] (3) The unit layer interval (d Å) of a hydrotalcite compound(particles) was measured by the RINT 2200V X-ray diffraction apparatusof Rigaku Co., Ltd.

Example 1

[0052] 19.94 g of magnesium oxide (commercially available product,content of 97%, BET specific surface area of 6.8 m²/g) and 0.5 liter ofdeionized water were placed in a 1-liter vessel and 0.125 liter of anaqueous solution of aluminum sulfate having a concentration of 1.04mol/l was added at room temperature under strong agitation by ahomomixer. After about 30 minutes of agitation, the resulting suspensionwas heated to carry out a reaction at 70° C. for 6 hours. After cooling[pH of the suspension was 7.15 (29.3° C.)], the suspension was filteredand washed. Thereafter, 1 liter of deionized water and the washedproduct were placed in a 2-liter vessel, fully dispersed and suspendedby a homomixer and heated at 70° C. A No. 3 water glass solution (0.104mol of SiO₂) was added to carry out an ion exchange reaction at 70° C.for 2 hours. After cooling, the reaction product was filtered, washedand dried at 95° C. for 20 hours. The yield of the dried product was37.4 g. After drying, the dried product was put through a 100-meshsieve. The porous hydrotalcite compound (sample H.T. -a-1) obtained bythe above method was represented by the following chemical formula 1.The physical properties of this hydrotalcite compound are shown in Table1 below.

Mg_(0.353)Al_(0.647)(OH)₂(HSi₂O₅)_(0.136)(SO₄)_(0.045)(OH)_(0.421).0.356H₂O  (chemicalformula 1)

Mg_(1.09)Al₂(OH)_(6.18)(HSi₂O₅)_(0.42)(SO₄)_(0.14)(OH)_(1.39).1.10H₂O  (compositionformula 1)

Example 2

[0053] 28.4 g of magnesium hydroxide (commercially available product,content of 98.5%, BET specific surface area of 30 m²/g) and 0.5 liter ofdeionized water were placed in a 1-liter vessel and 0.107 liter of anaqueous solution of aluminum sulfate having a concentration of 1.04mol/l was added at room temperature under strong agitation by ahomomixer. After about 30 minutes of agitation, the resulting suspensionwas heated to carry out a reaction at 90° C. for 4 hours. After cooling[pH of the suspension was 7.05 (30.3° C.)], the suspension was filteredand washed. Thereafter, 1 liter of deionized water and the washedproduct were placed in a 2-liter vessel, fully dispersed and suspendedby a homomixer and heated at 80° C. A No. 3 water glass solution (0.112mol of SiO₂) was added to carry out an ion exchange reaction at 80° C.for 2 hours. After cooling, the reaction product was filtered, washedand dried at 95° C. for 20 hours. The yield of the dried product was39.3 g. After drying, the dried product was put through a 100-meshsieve. The porous hydrotalcite compound (sample H.T.-a-2) obtained bythe above method was represented by the following chemical formula 2.The physical properties of this hydrotalcite compound are shown in Table1 below.

Mg_(0.486)Al_(0.514)(OH)₂(HSi₂O₅)_(0.131)(SO₄)_(0.071)(CO₃)_(0.004)(OH)_(0.232).0.445H₂O  (chemicalformula 2)

Mg_(1.89)Al₂(OH)_(7.78)(HSi₂O₅)_(0.51)(SO₄)_(0.28)(CO₃)_(0.015)(OH)_(0.91).1.73H₂O  (compositionformula 2)

Example 3

[0054] 18.86 g of magnesium oxide (content of 97%, BET specific surfacearea of 6.8 m²/g) and 2.12 g of zinc oxide (commercially availableproduct, BET specific surface area of 3.5 m²/g) were suspended indeionized water and the total amount was adjusted to 0.5 liter. Thissuspension was placed in a 1-liter vessel and 0.125 liter of an aqueoussolution of aluminum sulfate having a concentration of 1.04 mol/l wasadded at room temperature under strong agitation by a homomixer. Afterabout 30 minutes of agitation, the suspension was heated to carry out areaction at 90° C. for 4 hours. After cooling [pH of the suspension was7.21 (21.9° C.)], the suspension was filtered and washed. Thereafter, 1liter of deionized water and the washed product were placed in a 2-litervessel, fully dispersed and suspended by a homomixer and heated at 80°C. A No. 3 water glass solution (0.104 mol of SiO₂) was added to carryout an ion exchange reaction at 80° C. for 2 hours. After cooling, thereaction product was filtered, washed, dried at 95° C. for 20 hours andput through a 100-mesh sieve to obtain a porous hydrotalcite compound(sample H.T.-a-3) represented by the following chemical formula 3. Thephysical properties of this hydrotalcite compound are shown in Table 1below.

Mg_(0.295)Zn_(0.064)Al_(0.641)(OH)₂(HSi₂O₅)_(0.131)(SO₄)_(0.051)(OH)_(0.407).0.32H₂O  (chemicalformula 3)

Mg_(0.92)Zn_(0.20)Al₂(OH)_(6.24)(HSi₂O₅)_(0.41)(SO₄)_(0.16)(OH)_(1.27).H₂O  (compositionformula 3)

Comparative Example 1

[0055] A hydrotalcite compound comprising an interlayer anion which wassubstantially CO₃ ²⁻ (manufactured by Kyowa Kagaku Kogyo Co., Ltd.,trade name of DHT4) was represented by the chemical formula 4. Thissample was designated as H.T-b-1. The physical properties of thishydrotalcite compound are shown in Table 1 below.

Mg_(0.682)Al_(0.318)(OH)₂(CO₃)_(0.158)(SO₄)_(0.00143).0.557H₂O  (chemicalformula 4)

Mg_(4.28)Al₂(OH)_(12.56)(CO₃)_(0.99)(SO₄)_(0.009).3.5H₂O  (compositionformula 4)

Comparative Example 2

[0056] The physical properties of commercially available syntheticsilica (trade name of Fine Seal, manufactured by Tokuyama Corporation)are shown in Table 1 below. This sample was designated as S.I. TABLE 1average particle total pore average pore unit layer name of diameter BETvolume radius interval bulk 1) sample (μm) (m²/g) (ml/g) (nm) dÅ(loose/pat) Ex.1 H.T. −a-1 5.06 264 1.34 7.7 11.305 128/86  Ex.2 H.T.−a-2 5.99 175 0.87 7.3 11.135 90/76 Ex.3 H.T. −a-3 5.90 214 1.20 8.011.079 116/100 C.Ex.1 H.T. −b-1 0.67 13.1 0.05 8.7  7.642 45/36 C.Ex.2S.I. 10.1 292 3.7 10 — 102/91 

[0057] It is understood from Table 1 above that the porous hydrotalcitecompounds represented by the formula (I-a) of the present invention(Examples 1 to 3) have a larger BET specific surface area and moreexcellent pore characteristics with a large pore volume than thehydrotalcite compounds of Comparative Examples because they contain asilicic acid anion and a sulfuric acid ion, or a silicic acid anion in apart of exchangeable anions.

Example 4 Adsorption Test of Acidic Dye

[0058] 0.5 g of an adsorbent and 20 ml of a dye solution of NaphtholYellow S whose concentration has been adjusted were placed in a 100 mlErlenmeyer flask with stopper a common stopper and shaken untilequilibrium was reached at 30° C. (120 times/min). The resultingsolution was filtered and the amount of the residual dye in the filtratewas measured by an absorptiometer to obtain the amount and equilibriumconcentration of the adsorbed dye at that time. FIG. 1 shows the acidicdye (Naphthol Yellow S) adsorption isotherms of the hydrotalcitecompounds of Example 1 and Comparative Example 1 as an adsorbent.

[0059] It can be understood from FIG. 1 that the hydrotalcite compoundof the present invention is superior in acidic dye adsorptivity to theother hydrotalcite compound (Comparative Example).

Examples 5 to 7 and Comparative Examples 3 to 5 Evaluation of Ink JetRecording Medium

[0060] Preparation of Ink Jet Recording Medium:

[0061] The hydrotalcite compounds obtained in Examples 1 to 3 andComparative Example 1 above and synthetic silica (Comparative Example 2)were used to prepare ink jet recording media in accordance with thefollowing method.

[0062] 40 parts by weight of polyvinyl alcohol as a polymer adhesive, 5parts by weight of polyethyleneimine which is a cationic resin as anadditive and 0.02 part by weight of phosphoric acid as a neutralizerwere added to and mixed with 100 parts by weight of the hydrotalcitecompound or synthetic silica to obtain a coating solution having a solidcontent of 18 wt %. This coating solution was applied to paper by a No.20 bar coater and dried to obtain an ink jet recording medium.

[0063] Ink Jet Printing

[0064] Cyanogen (C), magenta (M), yellow (Y) and black (B) inks wereprinted on the obtained ink Jet recording medium by an ink jet recordingapparatus (trade name of BJ F200 of Canon Inc.).

[0065] Evaluation of Printing Properties

[0066] The (1) ink absorptivity (color development properties), (2)resolution, (3) water resistance and (4) light resistance of each inkjet recording medium were evaluated as follows.

[0067] (1) Ink Absorptivity (Color Development Properties)

[0068] A full color image formed on a printing sheet was observedvisually. The evaluation of ink absorptivity was carried out based onthe following criteria.

[0069] 5; The image has high density in all the colors and is clear.

[0070] 4; The image has high density in all the colors.

[0071] 3; The image has low density in some colors but has no practicalproblem.

[0072] 2; The image has low density in some colors.

[0073] 1; The image has low density in all the colors and is not clear.

[0074] (2) Resolution

[0075] All the dots were observed through an optical microscope(BHSM-313MU of Olympus Optical Co., Ltd.). The evaluation of resolutionwas carried out based on the following criteria.

[0076] 5; All the dots are very sharp.

[0077] 4; All the dots are sharp.

[0078] 3; Some dots are not sharp but there is no practical problem.

[0079] 2; Some dots keep their shape.

[0080] 1; None of the dots keeps their shape.

[0081] (3) Water Resistance

[0082] The printed surface was immersed in water for 1 minute and theblot of ink after drying was observed. The evaluation of waterresistance was carried out based on the following criteria.

[0083] 5; The dye of the printed portion does not run or blot on thepaper at all.

[0084] 4; The dye of the printed portion runs slightly but rarely blots.

[0085] 3; The dye of the printed portion runs slightly and blotsslightly but there is no practical problem.

[0086] 2; The dye of the printed portion runs and blots and the printedcharacters are hardly identified.

[0087] 1; The dye of the printed portion runs and blots considerably andthe printed characters cannot be identified.

[0088] (4) Light Resistance

[0089] Solid printing of cyanogen (C), magenta (M), yellow (Y) and black(B) inks was carried out and printed inks were exposed to light untilthe class 5 blue scale was discolored to a standard level using aSunshine weather meter (WEL-SUN-HC-B of Suga Shikenki Co., Ltd.) so asto measure and evaluate light resistance using a color differencecolorimeter (ZE-2000 of Nippon Denshoku Kogyo Co., Ltd.). The evaluationwas made based on a ΔE value.

[0090] ⊚; 0≦ΔE≦5

[0091] ∘; 5<ΔE≦10

[0092] Δ; 10<ΔE≦20

[0093] X; ΔE>20

[0094] Evaluation Results of Printing Properties

[0095] The evaluation results are shown in Table 2 below. In ComparativeExample 5, commercially available ink jet paper (Super Hi-grade KJ-1210of Kokuyo Co., Ltd.) was used. TABLE 2 ink water light resistance No.sample name absorptivity resolution resistance Y M C B Ex.5 H.T. −a-1 55 5 ⊚ ◯ ◯ ⊚ Ex.6 H.T. −a-2 5 5 5 ⊚ ◯ ◯ ⊚ Ex.7 H.T. −a-3 5 5 5 ◯ ◯ ◯ ⊚C.Ex.3 H.T. −b-1 2 2 3 ◯ Δ Δ Δ C.Ex.4 S.I. 3 2 2 ◯ X Δ ◯ C.Ex.5 — 5 4 5◯ X X Δ

Example 8

[0096] 0.313 liter of an aqueous solution of magnesium chloride having aconcentration of 1.37 mol/l and 0.095 liter of an aqueous solution ofaluminum sulfate having a concentration of 1.05 mol/l were mixedtogether in a 1-liter vessel and 0.380 liter of an aqueous solution of 3N sodium hydroxide was added at room temperature under agitation by ahomomixer. The obtained reaction suspension was transferred to anautoclave to carry out a reaction at 170° C. for 6 hours (pH of thecooled suspension was 9.92 (25.8° C.)). The temperature of thesuspension was raised to 80° C. again and a No. 3 water glass solution(0.133 mol of SiO₂) was added to carry out an ion exchange reaction at80° C. for 1 hour. After cooling, the reaction solution was filtered,washed, dried (95° C. for 20 hours) and put through a 100-mesh sieve toobtain a hydrotalcite compound represented by the following chemicalformula (5) (sample name of H.T.-a-4). The physical properties of thishydrotalcite compound are shown in Table 3 below.

Mg_(0.681)Al_(0.319)(OH)₂(HSi₂O₅)_(0.171)(SO₄)_(0.0512)(CO₃)_(0.0304).0.640H₂O  (chemicalformula 5)

Mg_(4.27)Al₂(OH)_(12.45)(HSi₂O₅)_(1.07)(SO₄)_(0.32)(CO₃)_(0.19).4H₂O  (compositionformula 5)

Example 9

[0097] Synthesis was carried out in the same manner as in Example 8before a hydrothermal treatment, a No. 3 water glass solution (0.033 molof SiO₂) was added to carry out an ion exchange reaction at 80° C. for 1hour, and the reaction product was cooled, filtered, washed, dried (95°C. for 20 hours) and put through a 100-mesh sieve to obtain ahydrotalcite compound represented by the chemical formula 6 (sample nameof H.T.-a-5). The physical properties of this hydrotalcite compound areshown in Table 3 below.

Mg_(0.685)Al_(0.315)(OH)₂(HSi₂O₅)_(0.0380)(SO₄)_(0.136)(CO₃)_(0.0158).0.634H₂O  (chemicalformula 6)

Mg_(4.35)Al₂(OH)_(12.45)(HSi₂O₅)_(0.24)(SO₄)_(0.86)(CO₃)_(0.10).4H₂O  (compositionformula 6)

Example 10

[0098] 0.7 liter of deionized water was placed in a 1-liter vessel and20 g of an oxide solid solution obtained by baking synthetichydrotalcite (manufactured by Kyowa Chemical Industry Co., Ltd., tradename of Kyoward 2200, MgO content of 59.1%, Al₂O₃ content of 34.7%) and8.63 g of synthetic amorphous silica (commercially available Tokuseal U,content of 94.58%) were added and suspended at room temperature underagitation by a stirrer. Thereafter, the resulting suspension wastransferred to an autoclave to carry out a reaction at 100° C. for 12hours. After cooling (pH of the suspension was 10.38 (27.7° C.)), thesuspension was filtered, washed, dried (95° C. for 20 hours) and putthrough a 100-mesh sieve to obtain a hydrotalcite compound representedby the following chemical formula 7 (sample name of H.T.-a-6). Thephysical properties of this hydrotalcite compound are shown in Table 3below.

Mg_(0.683)Al_(0.317)(OH)₂(HSiO₃)_(0.139)(HSi₂O₅)_(0.0856)(CO₃)_(0.0460).0.301H₂O  (chemicalformula 7)

Mg_(4.31)Al₂(OH)_(12.62)(HSiO₃)_(0.88)(HSi₂O₅)_(0.54)(CO₃)_(0.29).1.9H₂O  (compositionformula 7)

Example 11

[0099] 28.4 g of magnesium hydroxide (content of 98.5%, BET specificsurface area of 30 m²/g) and 0.6 liter of deionized water were placed ina 1-liter vessel and 84 ml of an aqueous solution of aluminum sulfatehaving a concentration of 1.02 mol/l was added at room temperature understrong agitation by a homomixer. After about 30 minutes of agitation,the resulting suspension was heated to carry out a reaction at 90° C.for 4 hours. After cooling (pH of the suspension was 7.22 (30.2° C.)),the reaction solution was filtered and washed. Thereafter, 1 liter ofdeionized water and the washed product were placed in a 2-liter vessel,fully dispersed and suspended by a homomixer, and heated at 80° C. A No.3 water glass solution (0.163 mol of SiO₂) was added to carry out an ionexchange reaction at 80° C. for 2 hours. After cooling, the reactionproduct was filtered, washed, dried (95° C. for 20 hours) and put to a100-mesh sieve to obtain a hydrotalcite compound represented by thefollowing chemical formula 8 (sample name of H.T.-a-7). The physicalproperties of this hydrotalcite compound are shown in Table 3 below.

Mg_(0.630)Al_(0.370)(OH)₂(HSi₂O₅)_(0.178)(SO₄)_(0.044)(CO₃)_(0.026)(OH)_(0.052).0.556H₂O  (chemicalformula 8)

Mg_(3.4)Al₂(OH)_(10.8)(HSi₂O₅)_(0.96)(SO₄)_(0.24)(CO₃)_(0.14)(OH)_(0.28).3.0H₂O  (compositionformula 8)

Example 12

[0100] 7.05 g of magnesium oxide (content of 97%, BET specific surfacearea of 5.2 m²/g) and 18.75 g of zinc oxide (commercially availableproduct, BET specific surface area of 3.5 m²g) were suspended indeionized water and the total amount was adjusted to 0.5 liter. Thissuspension was placed in a 1-liter vessel and 0.077 liter of an aqueoussolution of aluminum sulfate having a concentration of 1.04 mol/l wasadded at room temperature under strong agitation by a homomixer. Afterabout 30 minutes of agitation, the suspension was heated to carry out areaction at 90° C. for 4 hours. After cooling (pH of the suspension was6.32 (20.4° C.)), the reaction solution was filtered and washed.Thereafter, 1 liter of deionized water and the washed product wereplaced in a 2-liter vessel, fully dispersed and suspended by ahomomixer, and heated at 80° C. A No. 3 water glass solution (0.144 molof SiO₂) was added to carry out an ion exchange reaction at 80° C. for 2hours. After cooling, the reaction product was filtered, washed, dried(95° C. for 20 hours) and put through a 100-mesh sieve to obtain ahydrotalcite compound represented by the following chemical formula 9(sample name of H.T.-a-8). The physical properties of this hydrotalcitecompound are shown in Table 3 below.

Zn_(0.577)Mg_(0.01)Al_(0.412)(OH)₂(HSi₂O₅)_(0.185)(SO₄)_(0.054)(CO₃)_(0.003)(OH)_(0.113).0.247H₂O  (chemicalformula 9)

Zn_(2.80)Mg_(0.05)Al₂(OH)_(9.7)(HSi₂O₅)_(0.90)(SO₄)_(0.261)(CO₃)_(0.013)(OH)_(0.552).1.2H₂O  (compositionformula 9)

Comparative Example 6

[0101] A hydrotalcite compound (sample name of H.T.-b-2) containing aninterlayer anion which was substantially SO₄ ²⁻ was obtained in the samemanner as in Example 8 except that the reaction suspension before theion exchange of a silicic acid anion was dried and reduced in sizedirectly. The chemical formula of the compound is as follows. Thephysical properties of this hydrotalcite compound are shown in Table 3below.

Mg_(0.684)Al_(0.316)(OH)₂(SO₄)_(0.145)(CO₃)_(0.0126).0.664H₂O  (chemicalformula 10)

Mg_(4.33)Al₂(OH)_(12.66)(SO₄)_(0.92)(CO₃)_(0.08).4.2H₂O  (compositionformula 10)

Comparative Example 7

[0102] 80 parts by weight of the hydrotalcite compound represented bythe chemical formula 10 obtained in the above Comparative Example 6 and20 parts by weight of synthetic silica (trade name of Fine Seal,manufactured by Tokuyama Corporation) were mixed together. TABLE 3average particle total pore average pore unit layer name of diameter BETvolume radius interval bulk 1) sample (μm) (m²/g) (ml/g) (nm) dÅ(loose/pat) Ex.8 H.T. −a-4 0.81 16.4 0.036 3.4 10.402 67/54 Ex.9 H.T.−a-5 0.65 19.9 0.086 7.8 8.845 118/94  Ex.10 H.T. −a-6 1.20 62 0.61 0.611.663 60/47 Ex.11 H.T. −a-7 6.00 173 0.71 5.9 11.135 62/55 Ex.12 H.T.−a-8 8.20 98 0.67 9.6 10.756 43/38 C.Ex.6 H.T. −b-2 2.27 14.8 0.102 12.98.810 27/21

Examples 13 to 17 and Comparative Examples 8 and 9 Evaluation of Ink JetRecording Media

[0103] The hydrotalcite compounds obtained in Examples 8 to 12 andComparative Example 6 above and Sample M.I. X obtained in ComparativeExample 7 were used to prepare ink jet recording media in the samemanner as the ink jet recording media of Examples 5 to 7. The printingproperties of the ink jet recording media were evaluated similarly. Theresults are shown in Table 4 below. TABLE 4 ink water light resistanceNo. sample name absorptivity resolution resistance Y M C B Ex.13 H.T.−a-4 4 4 4 ⊚ ◯ ◯ ⊚ Ex.14 H.T. −a-5 4 3 4 ⊚ Δ ◯ ⊚ Ex.15 H.T. −a-6 3 4 5 ⊚Δ ◯ ◯ Ex.16 H.T. −a-7 5 4 5 ◯ ◯ ◯ ◯ Ex.17 H.T. −a-8 4 3 4 ◯ Δ ◯ ◯ C.Ex.8H.T. −b-2 3 2 3 Δ Δ Δ ◯ C.Ex.9 M.I.X. 2 1 2 Δ Δ Δ ◯

1. A dye fixing agent for water-color ink to be contained in thewater-color ink accepting layer of an ink jet recording medium having awater-color ink accepting layer formed on a substrate, which is ahydrotalcite compound containing a silicic acid anion and a sulfuricacid ion, or a silicic acid anion as an anion(s).
 2. The dye fixingagent for water-color ink according to claim 1, wherein the hydrotalcitecompound contains a silicic acid anion and a sulfuric acid ion, or asilicic acid anion in an amount of 10 to 98 mol % based on the total ofall the anions.
 3. The dye fixing agent for water-color ink according toclaim 1, wherein the hydrotalcite compound contains a silicic acid anionand a sulfuric acid ion, or a silicic acid anion in an amount of 20 to98 mol % based on the total of all the anions.
 4. The dye fixing agentfor water-color ink according to claim 1, wherein the hydrotalcitecompound contains a silicic acid anion and a sulfuric acid ion in anamount of 10 to 98 mol % based on the total of all the anions and asilicic acid ion in an amount of 5 to 100 mol % based on the total ofthe silicic acid anion and the sulfuric acid ion.
 5. The dye fixingagent for water-color ink according to claim 1, wherein the hydrotalcitecompound has an average particle diameter of 0.1 to 10 μm.
 6. The dyefixing agent for water-color ink according to claim 1, wherein thehydrotalcite compound is represented by the following formula (I):M^(II) _(1−x)Al_(x)(OH)₂(A₁ ^(n−))_(a)(A₂ ^(m−))_(b) .yH₂O  (I) whereinM^(II) is Mg²⁺ or/and Zn²⁺, A₁ ^(n−) is a silicic acid anion having avalence of n and a sulfuric acid ion (SO₄ ²⁻), or a silicic acid anionhaving a valence of n, with the proviso that the silicic acid anonhaving a valence of n is an anion selected from the group consisting ofSiO₃ ²⁻, HSiO₃ ⁻, Si₂O₅ ²⁻ and HSi₂O₅ ⁻, A₂ ^(m−) is an anion selectedfrom the group consisting of CO₃ ²⁻, NO₃ ⁻, Cl⁻ and OH⁻, x and y satisfy0.15<x≦0.80 and 0<y<2, and a and b satisfy 0.15<na+mb≦0.80.
 7. The dyefixing agent for water-color ink according to claim 1, wherein thehydrotalcite compound is represented by the following formula (I-a):M^(II) _(1−x)Al_(x)(OH)₂(A₁ ^(n−))_(a)(A₂ ^(m−))_(b) .yH₂O  (I-a)wherein M^(II) is Mg²⁺ or/and Zn²⁺, A₁ ^(n−) is a silicic acid anionhaving a valence of n and a sulfuric acid ion (SO₄ ²⁻), or a silicicacid anion having a valence of n, with the proviso that the silicic acidanion having a valence of n is an anion selected from the groupconsisting of SiO₃ ²⁻, HSiO₃ ⁻, Si₂O₅ ²⁻ and HSi₂O₅ ⁻, A₂ ^(m−) is ananion selected from the group consisting of CO₃ ²⁻, NO₃ ⁻, Cl⁻ and OH⁻,x and y satisfy 0.50<x≦0.80 and 0<y<2, and a and b satisfy0.50<na+mb≦0.80.
 8. The dye fixing agent for water-color ink accordingto claim 7, wherein in the above formula (I-a), the silicic acid anionand the sulfuric acid ion, or the silicic acid anion accounts for 10 to98 mol % of the total of all the anion (A₁ ^(n−)+A₂ ^(m−)).
 9. The dyefixing agent for water-color ink according to claim 7, wherein thehydrotalcite compound has a BET specific surface area of 50 to 400 m²/g.10. The dye fixing agent for water-color ink according to claim 7,wherein the hydrotalcite compound has a total pore volume (N₂ gasadsorption method) of 0.50 to 2.00 ml/g.
 11. The dye fixing agent forwater-color ink according to claim 7, wherein the hydrotalcite compoundhas an average pore radius (N₂ gas adsorption method) of 4 to 15 nm. 12.The dye fixing agent for water-color ink according to claim 7, whereinthe hydrotalcite compound has an average particle diameter of 0.1 to 10μm.
 13. The dye fixing agent for water-color ink according to claim 1,wherein the hydrotalcite compound is represented by the followinggeneral formula (I-b): M^(II) _(1−x)Al_(x)(OH)₂(A₁ ^(n−))_(a)(A₂^(m−))_(b) .yH₂O  (I-b) wherein M^(II) is Mg²⁺ or/and Zn²⁺, A₁ ^(n−) isa silicic acid anion having a valence of n and a sulfuric acid ion (SO₄²⁻), or a silicic acid anion having a valence of n, with the provisothat the silicic acid anion having a valence of n is an anion selectedfrom the group consisting of SiO₃ ²⁻, HSiO₃ ⁻, Si₂O₅ ²⁻ and HSi₂O₅ ⁻, A₂^(m−) is an anion selected from the group consisting of CO₃ ²⁻, NO₃ ⁻,Cl⁻ and OH⁻, x and y satisfy 0.15<x≦0.50 and 0<y<2, and a and b satisfy0.15<na+mb≦0.50.
 14. The dye fixing agent for water-color ink accordingto claim 13, wherein the hydrotalcite compound has an average particlediameter of 0.1 to 10 μm.
 15. An ink jet recording medium having anwater-color ink accepting layer formed on a substrate, wherein a dyefixing agent contained in the water-color ink accepting layer is the dyefixing agent of claim
 1. 16. The ink jet recording medium according toclaim 15, wherein the dye fixing agent is the dye fixing agent of claim6.
 17. The ink jet recording medium according to claim 15, wherein thedye fixing agent is the dye fixing agent of claim
 7. 18. The ink jetrecording medium according to claim 15, wherein the dye fixing agent isthe dye fixing agent of claim
 13. 19. A porous hydrotalcite compoundrepresented by the following formula (1): M^(II) _(1−x)Al_(x)(OH )₂(A₁^(n−))_(a)(A₂ ^(m−))_(b) .yH₂O  (1) wherein M^(II) is Mg²⁺ or/and Zn²⁺,A₁ ^(n−) is a silicic acid anion having a valence of n and a sulfuricacid ion (SO₄ ²⁻), or a silicic acid anion having a valence of n, A₂^(m−) is an anion selected from the group consisting of CO₃ ²⁻, NO₃ ⁻,Cl⁻ and OH⁻, x and y satisfy 0.50<x≦0.80 and 0<y<2, and a and b satisfy0.50<na+mb≦0.80.
 20. The porous hydrotalcite compound according to claim19, wherein the silicic acid anion having a valence of n is an anionselected from the group consisting of SiO₃ ²⁻, HSiO₃ ⁻, Si₂O₅ ²⁻ andHSi₂O₅ ⁻.
 21. The porous hydrotalcite compound according to claim 19,wherein the silicic acid anion and the sulfuric acid ion, or the silicicacid anion (A₁ ^(n−)) accounts for 10 to 98 mol % of the total of allthe anions (A₁ ^(n−)+A₂ ^(m−)).
 22. The porous hydrotalcite compoundaccording to claim 19 which has a BET specific surface area of 50 to 400m²/g.
 23. The porous hydrotalcite compound according to claim 19 whichhas a total pore volume (N₂ gas adsorption method) of 0.50 to 2.00 ml/g.24. The porous hydrotalcite compound according to claim 19 which has anaverage pore radius (N₂ gas adsorption method) of 4 to 15 nm.
 25. Theporous hydrotalcite compound according to claim 19 which has an averageparticle diameter of 0.1 to 10 μm.
 26. Use of the hydrotalcite compoundof claim 19 as a dye fixing agent contained in the water-color inkaccepting layer of an ink jet recording medium.